Judging by the number of readings on this topic, there are quite a lot of people who care about the public test server.
It is expected the Web UI compatible with other openEHR-based Servers (not only EHRBase, just like HAPI FHIR Server’s Web UI is compatible with other FHIR-based Servers. In other words, the Web UI connects to the EHRBase Servers, but it also can be switched to other [public] openEHR-based Servers.